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We report a systematic study of melting of layered lamella of silver alkanethiolates (AgSCn). A new synthesis method allows us to independently change the thickness of the crystal in two ways-by modulating chain length (n = 7-18) and by stacking these crystals to a specific layer number (m = 1-10). This method produces magic size lamella, having a well-spaced discrete melting point, Tm, distribution. Nanocalorimetry shows stepwise increases in Tm, as the lamella thickness increases by integer increments of chain length. The relationship between Tm and the inverse thickness follows the linear scaling law of Gibbs-Thomson effect. Layer stacking dramatically changes the degree and nature of size-effect melting. There is odd/even effect in stacked 2, 3, and 4 layers. Tm values of single-layer and multilayer samples do not show noticeable odd/even alternation. We develop a phenomenological model of size effect based on the cumulative excess free energy, G(excess), contributions of four spatially separate regions of the crystal: surface, Ag-S central plane, substrate interface, and interlayer interface. The selective appearance of the odd/even effect is due to the significant stabilization (1.4 kJ/mol) of interlamellae interfaces of odd-chain samples, possibly due to registration/packing. Stabilization occurs only for the mobile lamellae situated close to the free surface, and thus 2-layer samples show the highest degree of stabilization. X-ray diffraction shows that the chains are tilted 18° with respect to the basal plane normal but that the van der Waals gap is 0.3 Å smaller for crystals with odd chains.

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Approaching the ultimate limits of material sizes provides a route for designing new functional materials with extraordinary properties. We report the first systematic synthesis and characterization study of a wide range of highly ordered silver alkanethiolate (AgSCH or AgSCn, n = 1-16) aliphatic lamellae. Single crystalline multilayer AgSCn are synthesized by a modified solution reaction method. Hot toluene recrystallization or Ostwald ripening enhances the structural ordering of the lamellar crystals. This work approaches the chain length limit of aliphatic lamellae by synthesizing highly ordered AgSCn (n = 1-3) with extremely short chains. All lamellae form single crystals with well-registered interlayer interfaces, similar to other alkyl-based lamellae but different from polyethylene lamellae. AgSC2 with a layer thickness of 1.08 nm is the thinnest organometallic layer ever reported. The composition, morphology, decomposition and structure of the lamellae are comprehensively studied. A new method quantifies the composition of the residual Ag and AgS contents after the decomposition of the AgSCn: all of the Ag, none of the C and a fraction of the S remain in the residue. The structural orderings of the AgSCn crystals, which are probed by electron diffraction for the first time, are characterized in terms of chain conformation, interlayer lamellar ordering and intralayer lattice ordering. All AgSCn (n = 2-16) layers, except AgSC1, possess a common lattice packing and the same inorganic network structure.

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